The production of arylphosphines can be complicated if all of the substituents on the phosphorus atom are not identical. In situations where the production of mixed alkyl-aryl phosphines is desired, the method of production generally involves the use of at least one organo alkali metal intermediate, the synthesis of which is often difficult or inefficient.
One class of bidentate phosphorus ligands which are mixed alkyl-aryl phosphines has become of interest as a precursor of a catalyst composition useful in the production of a type of polymeric compound known as polyketones or polyketone polymers. These polymers are linear alternating polymers of carbon monoxide and at least one ethylenically unsaturated hydrocarbon. Such polymers have repeatinng units of the formula ##STR1## wherein B is a moiety of ethylenically unsaturated hydrocarbon polymerized through the ethylenic unsaturation. Such processes for the production of polyketones are illustrated by published European patent application Nos. 0,121,965 and 0,181,014. The processes generally involve the use of a catalyst composition formed from a compound of a Group VIII metal selected from palladium, cobalt or nickel, the anion of a strong non-hydrohalogenic acid and a bidentate ligand containing two Group VA atoms which are preferably phosphorus. Particularly useful as the bidentate phosphorus ligand is the mixed alkyl-aryl phosphine of the formula ##STR2## wherein R.sup.1 independently is an aryl group and R is a bridging divalent alkylene group, often the trimethylene group. Good results are obtained in the production of polyketones when the phosphine precursor of the catalyst composition is of the above formula wherein each R.sup.1 is phenyl and R is trimethylene, i.e., the ligand is 1,3-bis(diphenylphosphino)propane. One of the least complicated methods of producing this ligand is through the reaction of an alkali metal di(R.sup.1) phosphide, e.g., sodium diphenylphosphide, and an .alpha.,.OMEGA.-dihaloalkane such as 1,3-dichloropropane. Corresponding methods produce other bis(diarylphosphino)alkanes.
Recent process developments in polyketone production have shown that particularly good results are obtained on occasion of the bidentate ligand has at least one of the aryl groups and preferably each of the aryl groups substituted with a polar group, particularly an alkoxy group, in at least one position ortho or para to the phosphorus. Such bidentate phosphorus ligands are represented by the above formula wherein at least one R.sup.1 and preferably each R.sup.1 substituent is alkoxyphenyl wherein at least one position of the phenyl ring ortho or para to the phosphorus is substituted with alkoxy. Such diphosphines are produced in a generally preferred procedure by reaction of a dihaloalkane and an alkali metal di(alkoxyphenyl)phosphide wherein each phenyl has the ortho and/or para substitution. The ease and efficiency with which the alkali di(alkoxyphenyl)phosphide is produced, particularly if produced by reaction of alkali metal with the corresponding tri(alkoxyphenyl)phosphine, depends greatly on the location of the alkoxy substituents on the phenyl ring and to some extent the number of alkoxy substituents.
Production of alkali metal diphenylphosphide such as sodium diphenylphosphide by reaction of alkali metal and triphenylphosphine is well known and affords a good yield of phosphide. Such a process also works well with the production of alkali metal di(2-methoxyphenyl)phosphide from reaction of alkali metal and tri(2-methoxyphenyl)phosphine. Reaction of alkali metal and tri(4-methoxyphenyl)phosphine, however, does not give a satisfactory yield of alkali metal di(4-methoxyphenyl)phosphide. See copending U.S. patent application Ser. No. 07/175,021, filed Mar. 30, 1988 (titled Production of Ortho Substituted Dipehnylphosphides) for example. Accordingly, it would be of advantage to provide a process of broader applicability for the production of alkali metal di(alkoxyphenyl)phosphides wherein the phenyl has an alkoxy substituent in at least one of the ring positions ortho or para to the phosphorus.